You cannot - a XSD describes the DATA aspects e.g. of a webservice - the WSDL describes the FUNCTIONS of the web services (method calls). You cannot typically figure out the method calls from your data alone.
These are really two separate, distinctive parts of the equation. For simplicity's sake you would often import your XSD definitions into the WSDL in the <wsdl:types>
tag.
(thanks to Cheeso for pointing out my inaccurate usage of terms)
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